This invention relates to low drift spray nozzles and, more particularly, to spray nozzles and methods of spraying in which the liquid spray comprises large droplets.
In numerous applications it is important that liquid which is to be handled is discharged in a manner and in a condition in which drift is minimized. By way of example, one such application in which drift must be minimized is in the application of conventional herbicides, pesticides and other farm chemicals. Another such application in which drift is critical is in present day irrigation type rigs in which partially treated sewage is applied to the large tracts of land. Potential problems involved in the application of such sewage are not only limited to odor, but also viruses in the sewage might be carried by small droplets to adjacent localities if drift is not stringently controlled. To underscore the problems in such sewage applications, Federal as well as local agencies have arbitrarily set limits on the amount of drift which is permissible in such sewage irrigation installations. Under these limits, drift is generally confined to within 200 - 300 feet of the point of application and droplets which drift beyond this range are not acceptable.
In order to remain within these acceptable drift standards, irrigation sewage disposal equipment in the past have employed flooding or deflector type nozzles which are generally operated at very low pressures, frequently as low as 3 or 4 psig. At these low pressures, the generation of large droplets results and the generation of fine droplets, which could create a drift hazard, is minimized. Several important disadvantages, however, follow from the use of such low pressures. It is frequently difficult to obtain a good spray pattern with such low pressures and consequently coverage uniformity is at best minimal. Also, any variation in the supply pressure or pressure losses in the equipment itself due to frictional losses or pressure drop inherent in the piping, will cause a change in flow rate through the nozzles which adversely effects uniformity of coverage. Such pressure drops or losses are indeed common, as will be evident when it is considered that irrigation equipment is frequently in excess of 1000 feet in length and this equipment normally rotates about a pivot point with the extremities of the irrigation rigging often crossing terrain that is not completely level, causing pressure variations due to ground elevation. These variations due to ground elevation may be as great as 3 to 5 psig.
The nozzles and methods of the present invention overcome these disadvantages. In a nozzle and method incorporating the principles of the present invention, liquid pressures greatly in excess of those previously mentioned, may be utilized and yet the generation of large droplets which are not subject to drift may be optimized. Accordingly, since the method and nozzles of the present invention are capable of utilizing substantially larger line pressures, the adverse effect of changes in elevation, frictional losses and the like are minimized. In the nozzles and method of the present invention, line pressures may be employed, which if employed with the conventional nozzles heretofore utilized in the art, would produce extremely fine droplets which would drift substantial distances. Moreover, the nozzles and method of the present invention are capable of delivering liquid at widely ranging flow rates of more than 50 gpm to as little as 0.2 gpm without a substantial loss in droplet quality. Finally, nozzles and method incorporating the principles of the present invention result in substantially improved patternation definition and uniform distribution of droplet sizes.
In a principal aspect of the present invention, a nozzle comprises a first chamber having a fluid inlet, swirl means for imparting a swirling motion to the fluid in the first chamber, a second vortex chamber, first orifice means between the first and second chambers communicating the swirling fluid from the first chamber to the second vortex chamber, the second vortex chamber being larger in cross section than the first orifice means, and second orifice means at the end of the second chamber, the second orifice means being at least as large as the first orifice means for discharging the swirling fluid from the second vortex chamber.
In another principal aspect of the present invention, a method of producing large droplets of liquids comprises imparting a swirling motion to the liquid, passing the swirling liquid through a first orifice into a chamber which is larger in cross section than the first orifice and such that the liquid continues to swirl in the chamber, and discharging the swirling liquid from the chamber through a second orifice which is at least as large as the first orifice, whereby the discharged liquid comprises a plurality of large droplets.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.